The present invention relates to a folded flat-spring and its incorporation in a damper disc assembly, a damper device and a flywheel assembly.
In damper disc assembly, there are generally an input side member (such as clutch plates or the like), into which torque is input from an engine; and an output side member (spline hubs or the like), for outputting torque to an output side shaft, both are elastically coupled together In the rotational direction through an elastic member. The elastic member is typically made of coil springs which are expanded and compressed for damping torque variation.
In this case, it is necessary to reduce torsion rigidity in order to absorb low load torque variation. In general, in order to reduce the torsion rigidity of the coil springs, it has to decrease the diameter of the wire used in the coils. However, if the diameter of the wire used in the coils was decreased, torque transmission capacity would also be reduced. Accordingly, diameter of the coil springs must be increased in order to maintain a sufficient torque transmission capacity while suppressing the diameter of the wire used in the coils. Axial height of the coil springs would then also increased thereby adversely affecting the compactness of the damper disc assemblies.
A damper device is disposed, for example, between an engine and a transmission of an automotive vehicle for dampening torque variation of the engine. The damper device includes input and output side members which are rotatable relative to each other. coil springs for elastically coupling the input and output side members, and a vibration damper unit for dampening a torsional vibration generated during the power transmission.
Such a conventional damper device is disclosed in, for example, Japanese Patent Application Laid-Open No. 118124/1987. In this device, there are shown a first flywheel and a second flywheel which are rotatable relative to each other, coil springs for elastically coupling both the flywheels, and a viscous resistance generating mechanism interposed between the flywheels. The first flywheel is coupled with a member on the engine side, and the second flywheel is coupled with a clutch device on the transmission side. The damper device is equipped with the coil springs as elastic coupling mechanisms and a viscous resistance generating mechanism for damping the vibration.
In such an arrangement, the coil springs which are embodied in the damper unit require space In the circumferential and axial directions due to their intrinsic structure. Accordingly, it is particularly difficult to incorporate such a large damper device into a front wheel drive type vehicle where the axial space is restricted by many factors. Also, if the rigidity of the coil springs were to be reduced while maintaining a satisfactory torque transmission capacity, the axial height of the device would have to be unduly increased In the same manner as in the coil springs for damper discs described above.